Ultrasonic motors are known in the art and are powered by the ultrasonic vibration of a stator placed against the rotor or slider depending on the scheme of operation, namely rotation or linear translation. Resonance is used to amplify the vibration of the stator in contact with the rotor or slider.
One particular challenge with ultrasonic motors is that the friction power loss, structure dampening power loss and dielectric power loss all result in temperature elevations of the ultrasonic motor. This temperature change significantly affects the performance characteristics of the ultrasonic motor and changes the resonance frequency of the piezoelectric material making accurate control of the ultrasonic motor challenging.
U.S. Pat. No. 5,365,139 to Kasuga et al. discloses an electronic apparatus which is equipped with an ultrasonic motor. A driving pulse storage circuit stores driving pulses corresponding to the environment of the components of the ultrasonic motor. A stopping pulse storage circuit stores stopping pulses corresponding to the environment of the components of the motor. An environment detection means detects the environment of the components. An output pulse-selecting circuit receives the output signal from a driving pulse-generating circuit and the output signal from a stopping pulse-generating circuit and produces output pulses corresponding to the output signal from a detection signal-generating circuit to a piezoelectric vibrator-driving circuit. The moving member and the output means are operated by ultrasonic vibration of the vibrating member.
U.S. Pat. No. 5,258,694 to Ohnishi et al. discloses a control device for an ultrasonic motor for controlling to drive the ultrasonic motor according to a logical AND operation between a control pulse having a duty ratio changing from 100% to 0% according to a moving position of the ultrasonic motor and a driving signal having a resonance frequency of the ultrasonic motor. Accordingly, after starting the ultrasonic motor at a maximum speed, a moving speed of the ultrasonic motor can be gradually reduced until it reaches a target position, and when reaching the target position, the ultrasonic motor can be stopped precisely at the target position.
U.S. Pat. No. 6,894,422 to Kato discloses an ultrasonic-motor control system that includes an ultrasonic motor, a controller which starts the ultrasonic motor by changing a drive frequency of the ultrasonic motor from an initial drive frequency, a calculation device which calculates an initial drive frequency data based on a drive frequency at the commencement of rotation of the ultrasonic motor, and a setting device which sets the initial drive frequency based on the initial drive frequency data at a subsequent commencement of driving of the ultrasonic motor.
Although control systems for ultrasonic motors are known, improvements are desired. It is therefore an object to provide a novel ultrasonic motor control system and method.